mirror of
https://git.videolan.org/git/ffmpeg.git
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235 lines
5.9 KiB
C
235 lines
5.9 KiB
C
/*
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* MDCT/IMDCT transforms
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* Copyright (c) 2002 Fabrice Bellard
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <stdlib.h>
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#include <string.h>
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#include "libavutil/common.h"
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#include "libavutil/mathematics.h"
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#include "fft.h"
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/**
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* @file
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* MDCT/IMDCT transforms.
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*/
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// Generate a Kaiser-Bessel Derived Window.
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#define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation
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av_cold void ff_kbd_window_init(float *window, float alpha, int n)
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{
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int i, j;
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double sum = 0.0, bessel, tmp;
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double local_window[FF_KBD_WINDOW_MAX];
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double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n);
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assert(n <= FF_KBD_WINDOW_MAX);
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for (i = 0; i < n; i++) {
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tmp = i * (n - i) * alpha2;
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bessel = 1.0;
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for (j = BESSEL_I0_ITER; j > 0; j--)
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bessel = bessel * tmp / (j * j) + 1;
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sum += bessel;
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local_window[i] = sum;
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}
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sum++;
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for (i = 0; i < n; i++)
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window[i] = sqrt(local_window[i] / sum);
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}
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#include "mdct_tablegen.h"
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/**
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* init MDCT or IMDCT computation.
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*/
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av_cold int ff_mdct_init(FFTContext *s, int nbits, int inverse, double scale)
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{
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int n, n4, i;
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double alpha, theta;
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int tstep;
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memset(s, 0, sizeof(*s));
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n = 1 << nbits;
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s->mdct_bits = nbits;
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s->mdct_size = n;
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n4 = n >> 2;
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s->permutation = FF_MDCT_PERM_NONE;
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if (ff_fft_init(s, s->mdct_bits - 2, inverse) < 0)
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goto fail;
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s->tcos = av_malloc(n/2 * sizeof(FFTSample));
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if (!s->tcos)
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goto fail;
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switch (s->permutation) {
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case FF_MDCT_PERM_NONE:
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s->tsin = s->tcos + n4;
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tstep = 1;
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break;
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case FF_MDCT_PERM_INTERLEAVE:
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s->tsin = s->tcos + 1;
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tstep = 2;
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break;
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default:
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goto fail;
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}
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theta = 1.0 / 8.0 + (scale < 0 ? n4 : 0);
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scale = sqrt(fabs(scale));
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for(i=0;i<n4;i++) {
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alpha = 2 * M_PI * (i + theta) / n;
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s->tcos[i*tstep] = -cos(alpha) * scale;
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s->tsin[i*tstep] = -sin(alpha) * scale;
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}
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return 0;
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fail:
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ff_mdct_end(s);
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return -1;
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}
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/* complex multiplication: p = a * b */
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#define CMUL(pre, pim, are, aim, bre, bim) \
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{\
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FFTSample _are = (are);\
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FFTSample _aim = (aim);\
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FFTSample _bre = (bre);\
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FFTSample _bim = (bim);\
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(pre) = _are * _bre - _aim * _bim;\
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(pim) = _are * _bim + _aim * _bre;\
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}
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/**
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* Compute the middle half of the inverse MDCT of size N = 2^nbits,
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* thus excluding the parts that can be derived by symmetry
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* @param output N/2 samples
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* @param input N/2 samples
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*/
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void ff_imdct_half_c(FFTContext *s, FFTSample *output, const FFTSample *input)
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{
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int k, n8, n4, n2, n, j;
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const uint16_t *revtab = s->revtab;
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const FFTSample *tcos = s->tcos;
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const FFTSample *tsin = s->tsin;
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const FFTSample *in1, *in2;
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FFTComplex *z = (FFTComplex *)output;
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n = 1 << s->mdct_bits;
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n2 = n >> 1;
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n4 = n >> 2;
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n8 = n >> 3;
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/* pre rotation */
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in1 = input;
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in2 = input + n2 - 1;
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for(k = 0; k < n4; k++) {
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j=revtab[k];
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CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]);
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in1 += 2;
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in2 -= 2;
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}
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ff_fft_calc(s, z);
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/* post rotation + reordering */
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for(k = 0; k < n8; k++) {
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FFTSample r0, i0, r1, i1;
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CMUL(r0, i1, z[n8-k-1].im, z[n8-k-1].re, tsin[n8-k-1], tcos[n8-k-1]);
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CMUL(r1, i0, z[n8+k ].im, z[n8+k ].re, tsin[n8+k ], tcos[n8+k ]);
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z[n8-k-1].re = r0;
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z[n8-k-1].im = i0;
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z[n8+k ].re = r1;
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z[n8+k ].im = i1;
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}
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}
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/**
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* Compute inverse MDCT of size N = 2^nbits
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* @param output N samples
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* @param input N/2 samples
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*/
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void ff_imdct_calc_c(FFTContext *s, FFTSample *output, const FFTSample *input)
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{
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int k;
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int n = 1 << s->mdct_bits;
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int n2 = n >> 1;
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int n4 = n >> 2;
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ff_imdct_half_c(s, output+n4, input);
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for(k = 0; k < n4; k++) {
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output[k] = -output[n2-k-1];
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output[n-k-1] = output[n2+k];
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}
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}
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/**
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* Compute MDCT of size N = 2^nbits
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* @param input N samples
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* @param out N/2 samples
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*/
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void ff_mdct_calc_c(FFTContext *s, FFTSample *out, const FFTSample *input)
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{
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int i, j, n, n8, n4, n2, n3;
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FFTSample re, im;
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const uint16_t *revtab = s->revtab;
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const FFTSample *tcos = s->tcos;
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const FFTSample *tsin = s->tsin;
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FFTComplex *x = (FFTComplex *)out;
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n = 1 << s->mdct_bits;
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n2 = n >> 1;
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n4 = n >> 2;
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n8 = n >> 3;
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n3 = 3 * n4;
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/* pre rotation */
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for(i=0;i<n8;i++) {
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re = -input[2*i+3*n4] - input[n3-1-2*i];
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im = -input[n4+2*i] + input[n4-1-2*i];
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j = revtab[i];
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CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]);
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re = input[2*i] - input[n2-1-2*i];
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im = -(input[n2+2*i] + input[n-1-2*i]);
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j = revtab[n8 + i];
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CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]);
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}
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ff_fft_calc(s, x);
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/* post rotation */
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for(i=0;i<n8;i++) {
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FFTSample r0, i0, r1, i1;
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CMUL(i1, r0, x[n8-i-1].re, x[n8-i-1].im, -tsin[n8-i-1], -tcos[n8-i-1]);
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CMUL(i0, r1, x[n8+i ].re, x[n8+i ].im, -tsin[n8+i ], -tcos[n8+i ]);
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x[n8-i-1].re = r0;
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x[n8-i-1].im = i0;
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x[n8+i ].re = r1;
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x[n8+i ].im = i1;
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}
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}
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av_cold void ff_mdct_end(FFTContext *s)
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{
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av_freep(&s->tcos);
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ff_fft_end(s);
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}
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